1. Field of the Invention
This invention relates to a developing apparatus usable in an image forming apparatus.
2. Related Background Art
In an image forming apparatus such as a printer using the electrophotographic process, an electrophotographic photosensitive member, e.g. a photosensitive drum, which is an image bearing member, is uniformly charged, an electrostatic latent image is formed by selective image exposure to the photosensitive drum, the latent image is developed by a developing apparatus by the use of a toner which is a developer, the obtained toner image is transferred to a recording medium, and further the transferred toner image is fixed on the recording medium by heat and pressure to thereby obtain an image on the recording medium.
Such an image forming apparatus involves the supply of the toner to the developing apparatus and the maintenance of various process means, and as a method of facilitating the work of replenishing the toner and the maintenance, it has been put into practical use to put the photosensitive drum, charging means, cleaning means and the like together into a frame body and make them into a cartridge (process cartridge) detachably attachable to the main body of the image forming apparatus, and to make the developing apparatus into a cartridge (developing cartridge).
This developing apparatus made into a cartridge is provided with a frame body constituting a developing container having an opening portion at one end thereof and containing a toner therein, a developing roller (developer bearing member) rotatably disposed in the opening portion and bearing the toner thereon and carrying it to the photosensitive drum, a developing blade (developer regulating member) for regulating the amount of the toner borne on the developing roller, end portion seal members for preventing the leakage of the toner in the lengthwise direction of the developing roller at both end portions of the opening portion, and a flexible sheet member for preventing the blowoff of the toner from the gap between itself and the developing roller and between itself and the end portion seal members.
The flexible sheet member is attached to the lower portion of the opening portion of the developing frame body, and one end portion thereof opposite to the attached side thereof is a free end which bears against the entire area of the lower portion of the peripheral surface of the developing roller in the lengthwise direction thereof. The length of the flexible sheet member in the lengthwise direction thereof is up to a position entering and overlapping the end portion seal members, whereby the gap between it and the developing roller and between it and the end portion seal members is closed in the lower portion of the opening portion to thereby prevent the toner from blowing off from there.
The aforedescribed flexible sheet member, however, is sandwiched between the developing roller and the end portion seal members in the portion thereof overlapping the end portion seal members, and this has led to the problem that the developing roller is rotated, whereby the flexible sheet member is gradually pulled inwardly and outwardly laterally in the lengthwise direction and is deformed into a waving shape.
That is, as shown in FIG. 6 of the accompanying drawings, by the rotation of the developing roller 102 in the direction of arrow A, the flexible sheet member 106 is horizontally pulled in the same direction of arrow B as the direction of rotation of the developing roller 102. However, besides the horizontal pulling force in the direction of arrow B, inwardly and outwardly directed horizontal forces in the direction of arrow C and the direction of arrow D are also applied to the flexible sheet member 106 due to the vibration of the developing roller 102 and the misalignment of the rotary shaft thereof. Particularly in the portion wherein the flexible sheet member 106 and the end portion seal member 105 overlap each other, the pressure force of the flexible sheet member 106 to the developing roller 102 becomes great due to the repulsion of the end portion seal member 105 and therefore, this portion is liable to be affected by the aforementioned pulling forces in the direction of arrow C and the direction of arrow D.
In this case, in the area of the overlapping portion between the flexible sheet member 106 and the end portion seal member 105 against which the developing roller 102 does not abut, any force which urges the flexible sheet member 106 toward the end portion seal member 105 side does not work from the developing roller 102 side and therefore, when the pulling forces in the direction of arrow C and the direction of arrow D (particularly the direction of arrow D) work on the flexible sheet member 106, the flexible sheet member 106 is deformed and waves in that direction.
If the flexible sheet member 106 waves, there is formed a gap between the developing roller 102 and the flexible sheet member 106 and the toner becomes liable to leak from the gap. This problem arises more remarkably particularly when a non-magnetic toner is used as the developer, because the restraint of the toner by a magnetic force cannot be done.